White gold alloy

ABSTRACT

By including zinc, nickel, copper and cobalt in a 22 kt gold alloy, it is possible to obtain the desired white gold color in an alloy with satisfactory metallurgical properties and with reasonable raw material costs. More specifically, these elements are present in the following ranges: Gold≈91.67%; Zinc 0.4 to 1.5%; Nickel 6.0 to 7.5%; Copper 0.4 to 1.5%; Cobalt 0.02 to 0.50%. Master alloys and methods of making jewelry are also disclosed.

RELATED APPLICTAION

Under 35 USC §119(e)(1), this application claims the benefit of priorU.S. provisional application 60/410,671, filed Sep. 13, 2003, which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to gold alloys and more particularly to a rangeof novel 22-karat white gold alloy formulations.

BACKGROUND

White gold formulations possess a bright white platinum color. At ahigher karat values, their metallurgical properties may be inferior tomore common yellow gold alloys.

White gold was developed as an alternative to platinum when the RussianRevolution disrupted production of that metal during World War I. Whitegolds can be broadly classified into two categories: gold-palladiumalloys and gold-nickel alloys.

Palladium is added to gold (often with lesser amounts of silver, copperand zinc) to bleach the natural yellow color of pure gold to agray-white color. A generally accepted rule is that gold alloyscontaining greater than 15% (w/w) palladium are considered to be“white”. 22K (91.67% gold) alloys can contain a maximum of 8.33%palladium, resulting in a 9% palladium formulation that suffers from anundesirable off-yellow color and is much too soft in both the annealedand work hardened states to be fabricated into the most primitive ofjewelry products. Less than the maximum percentage of palladium in a 22Kwhite gold formulation balanced with additions of silver, copper andzinc does little to improve the hardness and degrades an already poorcolor.

In addition to technical issues with relatively high levels ofpalladium, financial considerations compound the manufacturing problems.In recent years the unit cost of pure palladium has often greatlyexceeded that of pure gold. Under these financial circumstances, a 22K(or even lower karat white gold alloys) containing a significantproportion of palladium as a bleaching agent will often exceed theintrinsic value of the same item in pure gold. This increased in costover the marked karat quality is without readily apparent benefit andmay be unacceptable to jewelry manufacturers and consumers alike.

As with palladium, nickel is added to white gold formulations to bleachthe natural yellow color of pure gold. Nickel-bearing white golds aremore popular for jewelry fabrication than the palladium containingalloys largely due to their lower cost. Unfortunately, when nickel isused in gold alloys in a sufficient weight percentage to bleach theyellow to the target gray/white color, the undesirable side effects ofmuch greater hardness and a marked reduction in ductility may occur inboth the work hardened and fully annealed states. Nickel-bearing whitegolds of acceptable color are so much harder and brittle as compared totheir yellow gold counterparts that many mechanical and hand fabricationtechniques cannot be applied to these materials. In general,nickel-bearing white gold alloys suffer from either from poormetallurgical properties or they have reasonable working properties withan off yellow color, or both.

In some cases poor color may be offset by electroplating the finishedproduct. Electroplating finished yellow-tinged “white” gold jewelry withrhodium to whiten the finished jewelry not only increases fabricationand intrinsic metal costs but presents a wide variety of stone setting,sizing, repair, usage and general wear issues. For example, a fingerring that must be increased in size often must be cut then stretched anda gold insert soldered into newly created opening. Rhodium platedjewelry will often blister and crack during cutting, stretching andsoldering. Even without cracking and blistering, all or part of the ringmust be re-plated after the mechanical sizing operations to standardizethe finish.

In summary, white gold jewelry fabricated from either palladium ornickel bearing alloys may suffer from a variety of technical and/orfinancial problems. Furthermore, as the gold karat quality increases,the weight percentage available for elements to bleach an increasingproportion of yellow gold and for other elemental additives decreases.For example, a 22 karat white gold alloys has only 8.33% of the alloyweight available for (1) bleaching the yellow gold color from 91.67% ofthe weight to an acceptable gray/white color and (2) developing alloymetallurgical characteristics consistent with standard jewelrymanufacturing techniques while maintaining a cost competitiveformulation.

SUMMARY

By including zinc, nickel, copper and cobalt in a 22 kt gold alloy, itis possible to obtain the desired white gold color in an alloy withsatisfactory metallurgical properties and with reasonable raw materialcosts. In general the resulting alloy has the following composition:gold 90.9-93.0% copper 0.4-0.8% nickel 6.0-7.5% cobalt 0.02-0.50% zinc0.50-1.0% More preferably, these elements are present in the following ranges:Gold≈91.67%; Zinc 0.5 to 1.0%; Nickel 6.0 to 7.5%; Copper 0.4 to 0.8%;Cobalt 0.02 to 0.10%. Typically cobalt is present at least as 0.03% byweight.

The above-described alloy can be produced using a master alloy andmixing the master alloy with gold in approximately a weight ratio thatprovides 90.9-93% gold (nominally 91.67% or 22 kt) with the remainingamount being the master alloy. The master alloy composition is (byweight): nickel   72-90%; zink  4.8-18.0% (preferably 6.0-12.0%) copper 4.8-18.0% (preferably 0.24-1.2%); and cobalt 0.24 to 1.2% (typicallycobalt is present at least as 0.4% by weight).

The invention also features methods of making jewelry having the aboveformulation.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DETAILED DESCRIPTION

An example of the new alloys according to my invention has the followingcomposition in weight percent: Gold 91.67% Zinc 0.66% Nickel 7.00%Copper 0.60% Cobalt 0.07% Total 100.00%

Bars, rods and finished jewelry products of the above composition have apleasing white color similar to platinum jewelry alloys without visibleyellow discoloration. Palladium electroplating of the finished piecesgenerally is not necessary to improve the color.

Bars cast from the above composition roll without cracking orintermediate annealing to 50% of the original thickness. After annealingat about 1425° F. for 15 minutes, the 50% reduced plates can again bereduced 50% in thickness without cracking or other problems.

Sheet can be rolled to thicknesses usual to jewelry stamping operationsand stamped into two and three-dimensional parts. Such parts can bethreaded or formed into springs using fabrication equipment and processcommon to lower karat yellow and white golds.

Wire made from the same composition can be drawn to diameters typicallyused for earring posts and chain production without the usual breakingand complicated annealing processes normally required for lower karatwhite golds.

In order to more easily prepare a uniform 22 k white gold composition, apre-alloy (“master alloy”) may be used. An example of the master alloyfor the new 22 k white gold composition in weight percent is: Zinc 7.92%Nickel 84.03% Copper 7.21% Cobalt 0.84% Total 100.00%

To prepare the new 22 k white formulation from the master alloy and finegold 8.33 weight parts of master alloy would be melted with 91.67 weightparts fine gold.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

1. A gold alloy comprising by weight about 90.9-93.0% gold and: 0.4 to1.5% zinc; 6.0 to 7.5% nickel; 0.4 to 1.5% copper; and 0.02 to 0.50%cobalt.
 2. The gold alloy of claim 1 comprising by weight: 0.5 to 1.0%zinc; 6.0 to 7.5% nickel; 0.4 to 0.8% copper; and 0.02 to 0.10% cobalt.3. The gold alloy of claim 2 in which the cobalt is present in about0.03 to 0.10% by weight.
 4. The gold alloy of claim 1 in which the alloycomprises by weight about: 0.66% zinc; 7.00% nickel; 0.60% copper; and0.07% cobalt.
 5. The gold alloy of any one of claim 1 in which the alloyconsists essentially of the listed elements.
 6. The gold alloy of anyone of claim 1 in which the gold is present in about 91.67%.
 7. A masteralloy for making a gold alloy composition, the master alloy comprisingby weight: 4.8 to 18.0% zinc; 72.0 to 90.0% nickel; 4.8 to 18.0% copper;and 0.24-6.0% cobalt.
 8. The master alloy of claim 7 comprising byweight: 6.0-12.0% zinc; 72.0 to 90.0% nickel; 4.8 to 9.6% copper; and0.24-1.2% cobalt.
 9. The master alloy of claim 8 in which the cobaltcomprises 0.4 to 1.2% by weight.
 10. The master alloy of claim 7 inwhich the alloy comprises about: 7.92% zinc; 84.03% nickel; 7.21%copper; and 0.84% cobalt.
 11. The master alloy of claim 7 in which thealloy consists essentially of the listed elements.
 12. A method ofmaking a gold alloy composition comprising providing the master alloy ofany of claims 7-10 and mixing the master alloy with gold in a ratio ofabout 90.9-93.0% by weight gold with the remainder being master alloy.13. The method of claim 12 in which the gold is present in about 91.67%by weight
 14. A method of making jewelry comprising manufacturing a goldalloy according to any of claims 1-4 in the form of a rod or a bar androlling the bar or rod to a sheet having a substantially reducedthickness.
 15. The method of claim 14 in which the sheet is stamped intoa two or a three-dimensional part.
 16. The method of claim 14 in whichthe sheet is manufactured into a threaded part.
 17. The method of claim14 in which the sheet is manufactured into a spring or aspring-containing part.
 18. Jewelry comprising the alloy of any ofclaims 1-4.
 19. Jewelry made by the method of claim 14.